In broad terms, photoelectric devices are devices that convert light energy to electric energy, or vice versa. For example, photoelectric devices include organic light emitting devices, inorganic light emitting devices, and solar cells.
In particular, among photoelectric devices, organic light emitting devices (organic light emitting diodes: OLEDs) have recently been in the spotlight according to a growing demand for flat panel displays.
An organic light emitting device is a device which converts electric energy to light energy by applying a current to an organic light emitting material. An organic light emitting device may have a structure in which a functional organic thin film is inserted between an anode and a cathode.
FIG. 1 is a cross-sectional view schematically showing an example of an existing organic light emitting device.
Referring to FIG. 1, the existing organic light emitting device includes an anode 20 as a transparent electrode layer, formed on a transparent substrate 10. An organic thin film layer 30 which sequentially includes a hole injection layer 31 and a hole transport layer 33, an organic light emitting layer 35, and an electron transport layer 37 and an electron injection layer 39, is deposited on the anode 20. A cathode 40 is formed on the organic thin film layer 30. Here, when a voltage is applied between the anode 20 and the cathode 40, electrons (e−) generated from the cathode 40 move to the organic light emitting layer 35 through the electron injection layer 39 and the electron transport layer 37. In addition, holes (H+) generated from the anode 20 move to the organic light emitting layer 35 through the hole injection layer 31 and the hole transport layer 33. Accordingly, electrons and holes collide and recombine to generate light in the organic light emitting layer 35.
Thus, the existing organic light emitting device is a current-driven device which controls light emitting efficiency using an organic thin film layer of several tens of nanometers which controls electron transport and hole transport, and adopts a diode structure. However, there are problems in that it is difficult to accurately control the thickness of each layer configuring the organic thin film, and light emitting characteristics are degraded due to the non-uniform thickness of the organic thin film.
In addition, since a metal thin film used as the cathode has a high surface light reflectance due to characteristics of the metal, external light flowing into the device may be reflected. There is a problem in that the reflected external light interferes with light generated from the organic light emitting device and degrades color expression.
To solve those problems, there are methods in which interference with the light emitted from the organic light emitting device is reduced by additionally attaching a polarizing plate or using a non-reflective electrode. However, since the polarizing plate cuts off portions of light generated from the inside, it degrades display efficiency.
Further, the existing organic light emitting device is formed on a substrate in which a driver device is already fabricated, and needs an additional driver circuit for stably driving a device as a current-driven device. However, the additional driver circuit reduces a light emitting area of a device, and thereby reduces an aperture ratio. In addition, since a driving voltage is increased to compensate for a decrease in brightness due to the reduction of the light emitting area, the life of device is shortened.